When placing lateral mass screws in the cervical spine it is desirable in certain situations to have the screw project into the bone upwardly and outwardly at an angle of approximately 30 degrees upward and 30 degrees outward. It is difficult to achieve such orientation with existing instrumentation without bending of the rod making up a part of the instrumentation. Presently available instrumentation does not permit optional screw placement and does not permit independent screw placement. Further, after presently available instrumentation has served its purpose and it is time for it's disassembly from the patient, disassembly is frequently difficult and time consuming. Still another problem with existing instrumentation is that it is relatively difficult to assemble and install. Further, there is not presently available for the cervical spine a system for fixing lateral mass screws to a rod. This invention is intended to address these problems.
The following references disclose instrumentation for fixation of the spine: U.S. Pat. No. 4,662,365 Gotzen et al.; U.S. Pat. No. 4,887,596 Sherman; U.S. Pat. No. 4,957,495 Kluger; and U.S. Pat. No. 5,254,118 Mirkovic. The following references disclose instrumentation for correcting various spinal deformities and related matters: U.S. Pat. No. 4,433,676 to Babechko; U.S. Pat. No. 4,773,402 to Asher et al.; U.S. Pat. No. 4,815,453 to Cotrel; U.S. Pat. No. 5,010,879 to Moriya et al.; U.S. Pat. No. 5,092,866 to Bread et al.; U.S. Pat. No. 5,147,359 to Cozad et al.; U.S. Pat. No. 5,147,360 to Dubousset; U.S. Pat. No. 5,154,718 to Cozad et al.; 5,181,917 to Rogozinski; 5,201,734 to Cozad et al.; 5,217,497 to Mehdian; 5,281,222 to Allard et al. and European patent application 0 452 792 Al.